The present invention relates to a technique for improving reliability of data written in a magnetic disk drive, and more specifically to a technique for improving reliability of recorded data against vibration of a write head caused by contact between a head/slider and a projection on a surface of a magnetic disk.
When a magnetic disk drive reads or writes data, a head/slider is allowed to fly above a rotating magnetic disk with a slight clearance therebetween (this clearance is described as flying height hereinafter). In order for a write head formed on the head/slider to be capable of accurately recording data by steadily magnetizing a magnetic layer of the magnetic disk, the flying height during the recording process must be within a prespecified range. When the flying height is too high, a magnetic flux from the write head does not sufficiently reach the magnetic layer, so that particles in the magnetic layer are not sufficiently magnetized and are not aligned in the desired direction. Therefore sometimes a sufficient output cannot be obtained during read operation of the recorded data, or the recorded data are degraded during passage of time even within a guaranteed period, which may sometimes disenable reading of the recorded data.
Recently, a magnetic disk drive is designed so that a flying height of a head/slider is as low as possible for achieving the high recording density. Therefore the possibilities of the head/slider to contact a small projection present on the surface of the magnetic disk more and more increase. The head/slider is required to fly and pivot with a prespecified flying height being raised by a lifting force of an air flow generated on the surface of the magnetic disk. Therefore the head/slider is supported by a suspension assembly having a flexible spring structure. Thus, when the head/slider comes into contact with a minute projection on a surface of the magnetic disk, a flying height of the write head may becomes larger, or a center of magnetization of the write head may displace from a recording position in a track, causing the off-track state.
In a magnetic disk drive, generally recorded data is not read for verification just after the data is recorded to prevent the performance from lowering. Therefore it is required that various conditions relating to reliability of recorded data be within prespecified ranges respectively. For this reason, in a case where the head/slider contacts any projection and the flying height becomes larger or where the off-track state occurs, it is desirable to interrupt the write operation until a flying height or a floating posture of the head/slider is returned to the normal state. To satisfy this requirement, it is necessary to detect fluctuations of the flying height and flying posture during the write operation.
Patent document 1 (Japanese Patent Laid-open No. 2001-23256) discloses a technique enabling a proper write operation in a magnetic optical disk even when vibrations occur. The magnetic disk drive includes an arm for positioning the write head at a position opposite to the magnetic optical disk with a prespecified clearance therebetween and a strain gauge for detecting a clearance between the magnetic optical disk and the magnetic head. When the strain gauge detects that the clearance between the magnetic head and the magnetic optical disk once becomes larger than a prespecified value and then returns to the normal value, the strain gauge supplies digital data after the clearance between the magnetic head and the magnetic optical disk becomes larger than the prespecified value again to the magnetic head.
Patent document 2 (Japanese Patent Laid-open No. 5-298812) discloses the technique for interrupting data write when the off-track state occurs during write operation of data in a sector of a track in a magnetic disk drive and then retrying the data write operation for writing data after interruption when the magnetic disk goes round. This document also discloses a technique for shortening the time required for rewriting data by resuming data write when the off-track state is restored to the normal state before the magnetic disk goes round once to reduce a volume of data to be rewritten.
Patent document 3 (U.S. Pat. No. 5,862,015) discloses a technique for detecting displacement of a suspension assembly from its neutral posture by means of a strain gauge attached to the suspension assembly. FIG. 8 in this document shows a technique for controlling a position of a head by supplying a signal obtained from a strain gauge attached to the end of a flexure tongue to a micro actuator adapted to move the flexure tongue in a lateral direction.